1. Field of the Invention
The present invention relates to a dipping apparatus, which can apply paste onto the ends of miniature components such as chip type electronic components with high accuracy.
2. Description of the Background Art
In general, a holding plate having a number of receiving holes is employed for efficiently applying electrodes to end portions of a number of chip type electronic components, as disclosed in U.S. Pat. No. 4,395,184. This holding plate comprises a hard substrate, a thin flat plate portion which is formed at a central portion of the substrate to be provided with a number of through holes, and a rubber-like elastic member which is embedded in a concave portion defined in the flat plate portion to be provided with receiving holes. The receiving holes pass through the elastic member and are smaller in diameter than the through holes. The holding plate elastically holds chip type electronic components in the receiving holes to partially project the same, so that electrode paste of silver or the like is uniformly applied to the projected portions. Thereafter the chip type electronic components are heated to dry the electrode paste.
The aforementioned U.S. Pat. No. 4,395,184 describes an exemplary method of applying electrode paste to such chip type electronic components with a roller. In this method, a holding plate holding chip type electronic components to partially project the same from its upper surface is carried by a conveyor, and a roller which is coated with electrode paste on its peripheral surface is brought into contact with the projected portions of the chip type electronic components to apply the electrode paste onto the chip type electronic components. In order to uniformly apply a thickness of the paste around the peripheral surface of the roller, a scraper is employed for scraping off the excess portion the paste while rotating the roller.
When the chip type electronic components are about 1.6 to 5.7 mm in length, for example, the electrodes have extremely small thicknesses of about 0.15 to 0.3 mm, which must be controlled with high accuracy. In the aforementioned method, however, the paste which is applied to the peripheral surface of the roller flows following rotation thereof, and hence the thickness of the paste is finely varied to cause dispersion in thickness of the electrodes which are formed on the chip type electronic components. Such dispersion may also be caused by vibration of the conveyor or fluctuation of the degree of horizontalness.
Japanese Patent Publication No. 3-44404 (1991) describes a method of coating the upper surface of a flat coating plate with a thin film of electrode paste and approaching a holding plate holding chip type electronic components to partially downwardly project the same to the coating plate for pressing the projected portions of the chip type electronic components against the coating plate, thereby applying the electrode paste to the chip type electronic components.
This method causes no such inconvenience as that described in the aforementioned method employing a roller. According to this method, the projected portions of the chip type electronic components are pressed against the bottom surface of the coating plate which is coated with the paste, whereby the projected portions of the chip type electronic components are prevented from dispersing in length and the electrode widths are uniformalized. However, a single holding plate generally holds thousands of chip type electronic components. An extremely strong reactive force acts on the holding plate when the chip type electronic components are pressed against the coating plate which is coated with the paste. Thus, the holding plate may be inclined to deviate from a parallel state with respect to the paste, or the, holding, plate itself may be deformed and its flatness deteriorated, leading to inferiority in accuracy durning application of the electrodes.